This invention relates to composite structures and, more particularly, to structures manufactured by the continuously wound filament technique. The invention further relates to a structure of the type described that is useful in the attenuation of noise in the intake of a conventional turbofan engine.
All modern jet engines incorporate acoustic treatment structure in the engine inlet. Conventionally, these elements are made with an inner perforated skin, a surrounding buried-septum honeycomb core, and a solid outer skin. The two skins are typically metal, usually aluminum, and the honeycomb core can either be aluminum or some composite material.
An aluminum perforated skin is subject to corrosion problems and also manufacturing problems in that the skin is originally manufactured as a solid aluminum sheet and then must be perforated prior to assembly with the core to make up the acoustic honeycomb panel. For both corrosion-resistance and weight considerations, it is desirable to utilize nonmetallic composite materials for the acoustic treatment panel; however, the typical woven composite sheet of graphite and some man-made material such as an aramid, for example, Kevlar, has the disadvantage that the solid sheet of composite material does not lend itself to easy perforation. The material tends to splinter when punched and drilling is a time-consuming procedure.
Therefore, it is an object of the present invention to provide an acoustic treatment structure manufactured from composite nonmetallic materials that is both lightweight and easy to manufacture when compared with conventional metallic acoustical treatment panels.